1. Field of the Invention
The invention relates to a muffler having a shell of a double-layer structure that has an inner shell that is formed by fixing ends of a tubularly rolled plate material to each other through a lock seam, and an outer shell that is formed substantially in the same manner as the inner shell.
2. Description of Related Art
As a muffler mounted on a vehicle or the like, there is a muffler of a double-roll lock seam structure. A shell of this muffler has a double-layer structure that has an inner shell as an inner layer, and an outer shell as an outer layer. Besides, a plate material is tubularly rolled, and ends of the plate material are fixed to each other through a lock seam to form each of the inner shell and the outer shell.
In this muffler, the water accumulated therein may enter a gap between the inner shell and the outer shell. Then, the water is heated by the heat of exhaust gas to be gasified. As a result, the pressure in the gap between the inner shell and the outer shell may rise to deform both the shells.
In view of this background, conventionally, there is known an art described in Japanese Patent Application Publication No. 2004-293538 (JP-2004-293538 A) in order to prevent such deformation of the shells. In Japanese Patent Application Publication No. 2004-293538 (JP-2004-293538 A), there is described a muffler having a structure as shown in FIG. 4. In this structure, a notch 52 is formed in an outer shell 53 at a position where the outer shell 53 overlaps with a lock seam portion 51 of an inner shell 50, and a gap between the inner shell 50 and the outer shell 53 communicates with the exterior of the muffler. Besides, in Japanese Patent Application Publication No. 2004-293538 (JP-2004-293538 A), there is also described a muffler having a structure as shown in FIG. 5. In this structure, a notch 54 is formed in the lock seam portion 51 of the inner shell 50, and the gap between the inner shell 50 and the outer shell 53 communicates with the interior of the muffler.
In each of these conventional mufflers, the pressure in the gap between the shells, which has risen due to the gasification of the water that has entered the muffler, is released from the notch 52 or 54. Thus, the pressure in the gap can be restrained from rising, and the shells can be prevented from being deformed.
However, in the case where the notch 54 is formed in the lock seam portion 51 of the inner shell 50, when a hole is formed through a region around the lock seam portion 51 of the outer shell 53 due to corrosion or a nick, the interior of the muffler and the exterior of the muffler immediately communicate with each other simply because of the formation of the hole.
Besides, in the case where the notch 52 is formed in the outer shell 53 as well, the region of the notch 52 is just as thick as a sheet of the plate material constituting the inner shell 50. Therefore, the interior of the muffler and the exterior of the muffler easily communicate with each other due to corrosion or a nick. Furthermore, since the gap between the inner shell 50 and the outer shell 53 is open to the outside, it is also feared that the water containing salt contents such as snow melting salt and the like may enter the gap from the outside to promote corrosion.